This disclosure relates to a continuous process for preparing an aqueous pigment dispersion. The aqueous pigment dispersion may be used, for example, to form toner compositions.
Toner utilized in development in the electrographic process, also known as a xerographic process, is generally prepared by chemical toner processes, in which nanometer size emulsion polymer and latex is mixed with a color pigment and other toner components during an aggregation process, followed by a coalescence process. A thermoplastic binder resin may be used in the aggregation process and may be several known polymers, such as polystyrenes, styrene-acrylic resins, styrene-methacrylic resins, styrene-butadiene resins, polyesters, epoxy resins, acrylics, urethanes and copolymers thereof. Carbon black is a common pigment used for toner compositions. Colored pigments such as red, blue, green, cyan, magenta, yellow, brown, and mixtures thereof, may also be used. Other toner components may be included, for example, wax and charge enhancing additives.
There are known processes and devices for preparing toner components used in toner compositions. For example, processes for producing resin emulsions useful in producing toners are described in U.S. Pat. No. 8,207,246 to Faucher et al., filed on Jun. 26, 2012, and U.S. Patent Application Publication No. 2011/0196066 to Faucher et al., filed on Feb. 5, 2010, the disclosures of which are totally incorporated herein by reference.
Current processes for preparing aqueous pigment dispersions for use, for example, in toner compositions, are performed in a batch process. Accordingly, because each individual batch process involves the handling of bulk amounts of material, each process takes many hours to complete before moving to the next process. In addition, batch-to-batch consistency is frequently difficult to achieve because of large variations of temperature, shear field, pumping capacity, and the like, throughout the stirred batch tank. Furthermore, it is difficult to scale-up the batches due to different batch reactions. The batch process also requires constant attention as an entire batch may have to be aborted if the batch process is out of control in terms of temperature, impeller speed, and the like.
Therefore, there is a need for processes with improved dispersion of toner components used in preparing toner compositions. In addition, there is a need for processes that provide more control of the particles produced, including maintaining quality, uniformity and size, without the extensive time and energy used in more conventional methods.